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I'll say something nice--
I think 27.5 x 4 might actually be a touch better than 26x4 in the winter.
I've always thought a 29 or 32 x 4 might be better than 26x5 on snow, and this is a tiny step in that direction.

Often what slows a snowbike down is not just not enough float, but all the energy needed to break trail. Skinnier, long contact patch tires with a huge diameter would seem to have an advantage, just like long skinny skis are better for touring.

So kudos to Trek for trying something new, even if it might not have my name on it, it's great to see more and more ideas and options.
 

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It's gonna be really tall, as tall as a 29+, so fit will be a problem with many fat bikes and it's gonna raise the BB a whole lot.

On my Mutz, the Trax Fatty 27.5 x 3.25 only leaves a short 1/2" of clearance at the bridges, so I couldn't run it. I could run them on my Jefe tandem, but I like 29+ on that ride.

Seems like a waste of molds, but you can't really complain about more choices :)

I'm more interested in B+ tires, we have plenty of 4-5" tires these days.
 

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Taller is not going to be better. I have 32" and 36" munis, the extra height puts your COG too high, so agility and slow speed performance are compromised. If you want "clearance", then a high BB 26 x 4-5 is your ticket.

I'll say something nice--
I think 27.5 x 4 might actually be a touch better than 26x4 in the winter.
I've always thought a 29 or 32 x 4 might be better than 26x5 on snow, and this is a tiny step in that direction.

Often what slows a snowbike down is not just not enough float, but all the energy needed to break trail. Skinnier, long contact patch tires with a huge diameter would seem to have an advantage, just like long skinny skis are better for touring.

So kudos to Trek for trying something new, even if it might not have my name on it, it's great to see more and more ideas and options.
 

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Taller is not going to be better. I have 32" and 36" munis, the extra height puts your COG too high, so agility and slow speed performance are compromised. If you want "clearance", then a high BB 26 x 4-5 is your ticket.
There's nothing taller about the 27.5x4 setup, maybe a 1mm difference in final diameter. So only is there no difference in that department, but you're not getting a narrower rim either to save weight and round out your tire profile.
I'll stick with the 26x4.8 and either build a set a Marge Lites as an option or wait for a 27.5 that makes sense - meaning 65mm.
The rides I've had on 4.8's haven't left me feeling the need for less tire though.
 

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Bad math.

The only way a 27.5 x 4" tire will not be taller than a 26 x 4" tire is if WTB makes it ;)

If Vee Rubber makes it, it'll be friggin tall as shite!!

There's nothing taller about the 27.5x4 setup, maybe a 1mm difference in final diameter. So only is there no difference in that department, but you're not getting a narrower rim either to save weight and round out your tire profile.
I'll stick with the 26x4.8 and either build a set a Marge Lites as an option or wait for a 27.5 that makes sense - meaning 65mm.
The rides I've had on 4.8's haven't left me feeling the need for less tire though.
 

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I honestly can't think of anything that I give less of a sh!t about, than 27.5x4.
 

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I honestly can't think of anything that I give less of a sh!t about, than 27.5x4.
Yeah, I am in this same camp.

I find myself asking, "why?" What is this supposed to do that 26x4 or 26x5 cannot? This screams to me a bike company trying to tell me what to buy, rather than offering something that riders actually want.

With regular 27.5 wheels, I can't tell a difference from 26. I'm pretty "meh" on those, too.
 

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if the overall diameter is the same on a 27.5x4 as a 26x4 and the width is the same isn't the contact patch the same? all you are doing is changing the sidewall. to me this seems like nothing more than a marketing ploy. the manufacturers saw how everyone went out and bought a fat bike and now they want to get everyone to but this new size. i see no advantage and as others have pointed out less cushion with the short sidewall. Now if the OD is taller so the 27.5 tire has the same sidewall as the 26 then there would be an advantage. not sure how much of one plus the addition of the extra weight may negate the advantage. either way i will not be jumpin into the 27.5x4 market.
 

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if this is true then your contact patch is most likely smaller on the 27.5 due to the narrower tire given the relative tire pressures. there is then no advantage.
 

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I don't see any point to this either unless we're talking a 27.5 x 65mm rim. Now we're getting somewhere. That would yield a rounder tire profile on the 4" tire and actually save weight instead of adding it while maintaining the overall diameter and bb height.

Keeping the 80mm rim width with the 27.5" rim on the other hand really makes the whole endeavor a wash at best IMO, at worst an actual disadvantage of only a minor one. We shall see. However in true MTBR fashion most who forked out the cash for those models will spew about how much of a difference it makes no matter what.
 

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I really wanted to post about Trek's new expandable rim coupler that allows you to switch between 26 and 27.5, but thought better to not.
 
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